This invention relates generally to micro-optical devices and optical beam steering and more particularly to a continuously variable analog micro-mirror device.
There are many applications for light-beam steering devices that have high spatial and time resolution and high brightness, including applications in display of information for education, business, science, technology, health, sports, and entertainment. Some light-beam steering devices, such as digital light-mirror arrays and deformographic displays, have been applied for large-screen projection. For white light, light modulators such as the reflective digital mirror arrays have been developed with high optical efficiency, high fill-factors with resultant low pixelation, convenient electronic driving requirements, and thermal robustness.
Macroscopic scanners have employed mirrors moved by electromagnetic actuators such as xe2x80x9cvoice-coilsxe2x80x9d and associated drivers. Micro-mirror devices have used micro-actuators based on micro-electro-mechanical-system (MEMS) techniques. MEMS actuators have also been employed in other applications such as micro-motors, micro-switches, and valves for control of fluid flow. Micro-actuators have been formed on insulators or other substrates using micro-electronic techniques such as photolithography, vapor deposition, and etching.
A micro-mirror device can be operated as a light modulator for amplitude and/or phase modulation of incident light. One application of a micro-mirror device is in a display system. In such a system, multiple micro-mirror devices are arranged in an array such that each micro-mirror device provides one cell or pixel of the display. A conventional micro-mirror device includes an electrostatically actuated mirror supported for rotation about an axis of the mirror into either one of two stable positions. Thus, such a construction serves to provide both light and dark pixel elements corresponding to the two stable positions. For gray scale variation, binary pulse-width modulation has been applied to the tilt of each micro-mirror. Thus, conventional micro-mirror devices have frequently required a high frequency oscillation of the mirror and frequent switching of the mirror position and thus had need for high frequency circuits to drive the mirror. Binary pulse-width modulation has been accomplished by off-chip electronics, controlling on- or off-chip drivers.
Conventional micro-mirror devices must be sufficiently sized to permit rotation of the mirror relative to a supporting structure. Increasing the size of the micro-mirror device, however, reduces resolution of the display since fewer micro-mirror devices can occupy a given area. In addition, applied energies must be sufficient to generate a desired force needed to change the mirror position. Also, there are applications of micro-mirror devices that require positioning of the mirror in a continuous manner by application of an analog signal rather than requiring binary digital positioning controlled by a digital signal. Accordingly, it is desirable to minimize a size of a micro-mirror device so as to maximize the density of an array of such devices, and it is desirable as well to provide means for positioning the micro-mirror device in an analog fashion.
Some micro-mirrors have used a liquid-metal drop to support the mirror. Such a support allows the micro-mirror to adopt various positions in a continuous range, with tilting about axes with many different orientations.
While the various beam-steering devices have found widespread success in their applications, there are still unmet needs in the field of micro-optical beam steering, particularly for continuous-range analog beam steering.